Previous studies in our laboratory have shown that carnitine is able to stimulate glycerol release from adipose tissue of human newborns and to potentiate glycerol release in the presence of lipolytic agents in adult adipose tissue and isolated fat cells from both humans and rats. Preliminary data indicate that carnitine is acting by preventing the decrease in cyclic adenosine 3':5'-monophosphate (cyclic AMP) accumulation caused by free fatty acids. Carnitine uptake by rat fat cells is increased by norepinephrine and decreased in the presence of insulin. In addition, a carnitine palmityl transferase-like activity has been detected in the plasma membrane of fat cells. These data indicate that carnitine may be involved in the transport of free fatty acids through the plasma membrane of fat cells and if so would provide a locus for insulin to exert into antilipolytic action. The main objective of this proposal is to determine the precise mechanism of action of carnitine on fat cell metabolism. The effect of carnitine on the enzymes responsible for cyclic AMP accumulation (adenylate cyclase and phosphodiestease) will be studied to determine if carnitine has a direct effect of cyclic AMP accumulation in addition to its indirect effect of preventing inhibition of cyclic AMP accumulation by free fatty acids. In addition, the role of carnitine on free fatty acid release from fat cells as well as the possible involvement of insulin in his process will be studied. Further work on the acyl carnitine transferase-like activity in the plasma membrane of fat cells will be the first step in this portion of the proposed studies. The role of insulin in this system will be studied as well as the effects of insulin and carnitine on glucose metabolism in isolated fat cells.